Relatively recently, infusion ports or portals have been developed which can be implanted in the body and remain there for a prolonged period of time by being serviced percutaneously without having to be removed from the body. Infusate is injected into the port by means of a conventional hypodermic syringe.
Known infusion devices of this general type have an infusate chamber formed within a housing of cup-like configuration with a top end closed by a needle-penetrable, resealable septum. The septum is typically a flat block of rubber contained, for example, axially within a cylindrical channel formed near the open end of the housing. With this arrangement, the exposed surface of the septum is generally recessed within the housing. The chamber is situated immediately below the septum for receiving the infusate. The infusate is delivered to a desired site within the patient by means of a catheter connected to a hollow stem leading from the chamber.
Typically, such infusion devices are made by first joining the stem to an open-ended, cylindrical wall of the housing. This is often accomplished by electron beam welding the stem along the inside of the cylindrical wall. In this operation, the welding head typically directs the electron beam through the open bottom end of the housing wall against the inner end of the stem to form a continuous weld bead. Then, the weld area is cleaned and polished to remove all traces of weld debris. When this is done, the septum is inserted into the housing from below, and positioned so as to close the top end. A top wall of the housing channel extends partially over the top of the septum and a ledge in the channel engages under the septum to prevent the septum from being dislodged vertically. Subsequently, the bottom end of the housing is closed by a base plate which is welded into place all around the housing. The base's external weld seam area is then cleaned.
This method of construction, and particularly the welding and finishing operations, tends to be exacting, tedious and expensive. Needless to state, the welds must be fluid impervious to prevent leakage of infusate from the housing. Furthermore, the quality of the finish of the weld seam about the base plate must be assuredly high to avoid sites conducive to bacterial growth after implantation. A complication in welding and finishing the base plate's weld seam is the presence of the septum. Extreme care must be taken not to damage or contaminate the septum during these procedures, making automated manufacture of such devices quite difficult, if not impossible.
While such prior art infusion ports are generally suitable for their intended purpose, although not entirely satisfactory, certain inherent limitations and inadequacies have been identified.
It is apparent from the foregoing description that if the infusion device is to have a long service life after it is implanted in the body, the penetrable septum must be capable of retaining its sealing properties even after a large number of injections. In other words, the hypodermic needle used to inject the infusate into the device must not "core" the septum so as to create possible avenues of leakage therethrough.
Also, when injecting infusate into the portal it is important that the hypodermic needle completely penetrate the portal's septum with only one puncture of the patient's epidermis to avoid undue discomfort to the patient and to assure that the infusate being injected flows into the device's chamber as it is supposed to, rather than being deposited locally in the patient's body and causing possible harm to the patient. Bearing in mind that such implantable devices actually move to some extent in the patient's body and may be situated at different depths below the skin depending upon the weight of the patient, proper targeting of the hypodermic needle on the infusion device's penetrable septum is not a simple matter. This is all the more the case considering that it is desirable to make implantable devices of this type as small and compact as possible so as to occupy a minimum amount of space in the body. Not only that, but the arrangement by which the septum is retained typically restricts the exposed surface of the septum to a mere fraction of its total area, making it an even smaller target.
Another disadvantage arises out of the configuration of the top end of the housing in which the septum is seated. By virtue of the fact that the septum is recessed in the housing, a generally flat surface is presented to the skin of the patient. This creates the opportunity for seroma or pocket formation at the top of the device. Such a dead space may collect body fluid thereby promoting bacterial growth and infection or collect fibrin that can interfere with access to the chamber. Such an irregular, unyielding surface at that end of the portal also raises the potential for abrasion and tissue breakdown if palpation is used to locate the infusion port in order to service it.